Hi all,
One opto switch stopped working on my scared stiff, #36 right popper. Opto theory in manual says the Transmitter should always be around 1.4 volts. This non functional one is measuring 25 volts!

I noticed immediately that the tiny board looks burnt. I took it apart anyway and reflowed the solder to reseat the LED. Still, switch is not working.

To me it seems the opto is fried, but what came first? Did the transmitter fry because the voltage to it is 25 volts? Or is voltage now high because the LED/ tiny board is toasted?

I'm hesitant to replace the opto only to have it get 25 volts and fry again? Or is that normal voltage and once a fresh LED and board are in, it will get back to 1-2 volts?

Thanks for the help!

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Thanks for the pointer. This is the first time I've had an opto issue and the manual has clear schematics, but I'm not exactly sure what to check.
The two leads powering this opto switch are J206-3 (column) and J208-7 (row). These are located on the CPU board assembly, but it's just the source for the switch matrix - do I unplug the two plugs and touch the multimeter to the pins directly on the board?

Also I see in the manual a 16 OPTO PCB board layout and the associated wiring schematic. Is this what controls voltage to all the optos? There are resistors everywhere. The fact the voltage is so high at the opto could mean a resistor is shot, no? But now I don't know how to find which resistor it might be?

Thanks again everyone for any ideas!

Thanks for the follow up comment - to be honest, I really don't know what I'm looking for - and I didn't realize the transmitters aren't involved with switch matrix layout. This is all starting to make sense now.

Ok so, the high voltage at the opto Transmitter is (most likely?) a result of an issue with the 16-opto board (under the playfield). Can it be that just a resistor on the opto board has either blown or is now detached from the board at a solder point?

Regarding the wiring schematics and the 16-optoboard layout, how can I know what resistor I should look at? In other words, how can I find out what resistor controls this particular blown opto transmitter?

Thanks so much guys, I'm learning a lot with this troubleshooting process. When I get some time this weekend I'll look at the 16-opto board in more detail.

Thanks for all the help guys, and also for the very detailed colored schematic with the short, and the nice explanation .
I finally got around to troubleshooting today, and now I have to admit I must have missed something the first time. I powered up and all voltage seemed okay at the 16 opto board. Then I rechecked the leads on my problematic transmitter, it read 12 volts. Not 25... I triple checked the opto board and everything seemed fine regarding voltage.

So, I took out the opto and upon close inspection, I noticed one of the leads (legs?) of the led was missing (between the LED base and the board)! So with age/time maybe it got weak and just burned/broke off? Check out the picture.

With only 12v (and not 25v) at the leads, I felt more comfortable installing a new opto and mini board. Put it all back together and now everything works fine (second image, lit opto)

Thanks again for the great support, this is the main reason I appreciate this forum. Cheers from Switzerland,
Tom

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